Conventionally, in an ore sorting factory or a stone crushing factory, a screen called a grizzly apparatus is used to remove mud from raw stone and deliver the raw stone which is free from mud to a hopper. Typically, the grizzly apparatus includes a plurality of grizzly bars arranged in parallel at predetermined intervals corresponding to screen openings and disposed with an inclination angle of 35 to 45 degrees with respect to a horizontal direction. Patent Literature 1 discloses such a grizzly apparatus.
The grizzly apparatus disclosed in Patent Literature 1 includes a plurality of rollers arranged in parallel at predetermined intervals at a feeding part of a raw stone hopper, and a plurality of separators disposed above the rollers. Two adjacent rollers of the plurality of rollers form a pair. The pair of rollers are driven to rotate in opposite directions. Between the pair of rollers, a slit used to sort out the raw stone is formed. Between two adjacent pairs of rollers, a gap is formed. The separator is disposed to cover the gap formed between two adjacent pairs of rollers, and has a shape in which a rectangular plate is folded in two to form an upwardly protruding part. This separator serves to guide the raw stone to the slit formed between the pair of rollers.